The structure, organization and development of the olfactory system will be studied with a variety of normal and experimental methods, including the autoradiographic method and horseradish peroxidase method of demonstrating axonal connections, as well as the electron microscope. Most of the projects are directed at the olfactory cortex of the rat including analyses of the organization of the axonal projection to this cortex from the olfactory bulb, the organization of the association and commissural fibers within the cortex, and the cells of origin of extrinsic projections to other parts of the brain. In addition, the development of the afferent connections will be analyzed by studying the effect of partial lesions of the olfactory bulb at the time of birth, and by following the electrophysiological responses of the cortex during the first two weeks following birth. In addition the efferent connections of the several cytoarchitectonic areas within the prefrontal cortex of the rat and cat will be studied, with emphasis on the areas which have been previously defined as receiving projections from the olfactory cortex or amygdala.